The cost of a microcomputer as currently used to solve complex control problems depend to a great extent on the number of terminals through which signals are conductable to the microcomputer and through which control signals for the control of loads can be transmitted from the computer. The problem in controlling these costs is to lay out the entire circuit arrangement in such a way that a less expensive microcomputer with a smaller number of terminals can be used. One possible solution to this problem is by combining switches to form groups so that their switching positions can be detected via fixed-cycle interrogation pulses. A system of this kind has been described by the German specification No. OS 2 815 234. Another solution to this problem is to control particular loads in multiplex operation.
From the German specification No. OS 3 207 633, it is known that check pulses may be generated during a program run for supervising the functioning of a microcomputer. These check pulses may be picked up on one terminal of the microcomputer to trigger a retriggerable monostable multivibrator. If the check pulses on the input of this monostable multivibrator do not appear in given time intervals, the multivibrator is no longer triggered and the potential on the output of the multivibrator connected with the reset input of the microcomputer is changed, the change of potential indicating an error in the program run. At present such check pulses are picked up on a terminal of the microcomputer which is not used for the control of other functions.
In circuit arrangements for the control of a seat adjusting device in motor vehicles, the adjusting motors or the relays controlling these adjusting motors have been connected to separate terminals of the microcomputer. An embodiment of this kind is shown in the German specification No. OS 3 037 193. If it is assumed that four adjusting motors are used in a particular seat adjusting device, and the adjusting motors are controllable via eight relays for both directions of rotation, eight terminals are necessary to control these motors. An additional grouping of eight terminals to supervise the input switches is also needed. In a circuit arrangement of this kind a microcomputer with 32 terminals is necessary, so that the other necessary functions can also be carried out.
Also noted in U.S. Pat. No. 4,463,426 issued July 31, 1984 to Caddick et al. for microprocessor controlled vehicle seat position control.